Method of definning sand cores



March 22, 1960 o. w. BRANDT ETAL 2,929,120

METHOD OF DEFINNING SAND CORES Filed Dec. 4 1957 v INVENTORS Q 4;

ATTOA EV METHGD F DEFTNNING SAND (IORES Otto W. Brandt, Rochester, andPhilip West, St. Clair Shores, Mich, assignors to General Meters(Iorporation, Detroit, Mich, a corporation of Delaware ApplicationDecember 4, 1957, Serial No. 7%,583

4 Claims. (0. 22--194) This invention relates to preparing and cores formetal casting operations and more particularly to a method of removingfins formed on the surface of such sand cores during the productionthereof.

A typical mold or core box used in making dry sand cores is formed oftwo halves. When the two halves of the core box do not mate accuratelythe inner surfaces of the core box which define the core-forming cavityare not uniform and continuous at the junction of the core box halves. Aspace or gap in these surfaces therefore exists adjacent the abuttingedges of the core box half. During the core-blowing operation, sandaccumulates in this space and forms a thin ridge on the surface of thecore. The shape and size of this ridge depend upon the accuracy of themating of the core box halves. Hence, excessive finning is found oncores made from poorly mated core box halves and on cores made inextensively used core boxes which have been worn into a poorly fittingrelationship.

Generally, at least a small amount of finning occurs in the molding ofmost sand cores and a subsequent definning operation is usuallynecessary. Heretofore, it

has been customary in the art to remove fins from sand core surfacesemploying slow, crude mechanical operations such as hand abrading orstriking the fin with a suitable implement so as to break the fin fromthe core body. These methods of definning the core merely chip .away thefin and often leave a ragged portion of the fin. Moreover, these methodsinvolve excessive handling of the cores, which often causes breakagethereof or damages the surface of the core so that it is unfit for use.In

addition, complex cores cannot usually be satisfactorily definned bythese methods since some fins are in inaccessible recesses in the core.Prior to the present in- .vention, therefore, it Was necessary toproduce complex sand cores with more costly precise techniques in orderlto insure that excessive deleterious finning did not occur.

Accordingly, it is an object of the present invention to provide amethod for rapidly definning sand cores and which reduces the handlingand breakage thereof. An-

other object of the invention is to provide a method of definning sandcores which can be employed to defin complex sand'cores. A still furtherobject of this invention is to provide an automatic method of definningsand cores ,by a low pressure sand blast.

Briefly, in accordance with this invention, fins on the surface of sandcores are removed by means of a low pressure sand blast treatment. Aconventional sand blast nozzle is employed to direct a blast of sandunder low air pressure upon the surface of a sand core substantiallyperpendicular to a major surface of a fin.

- Other objects, features and advantages of the present invention willbecome more apparent from the following description of preferredembodiments thereof and from ;the figures, in which:

Figure 1 is a somewhat schematic elevational view in 2,2,l2 PatentedMar. 22, was

Figure 2 is an enlarged fragmentary sectional view of a finned sand coreduring sand blasting; and

Figure 3 is a view similar to Figure 2 of a sand core 7 after thedefinning operation.

Sand cores are conventionally formed of a suitable mixture of sandsderived from lake beds or from the shores of rivers, lakes, etc.,respectively referred to as lake sand and bank sand. Typically, amixture of 50% lake sand and 50% bank sand is used, although in someinstances pure silica sand is employed. The sand is mixed in a drycondition with a suitable cereal binder such as corn meal, wood pitch,corn flour or the like. After the cereal binder has been homogeneouslydistributed throughout the dry sand, approximately 2% by weight of wateris uniformly combined with the mixture. Thereafter, a core oil binder,such as linseed oil, corn, oil, soybean oil or hempseed oil is normallyadded and thoroughly blended into the sand mixture. The relative amountsof the binder and core oil can vary, and the specific proportionsthereof are dependent upon the desired characteristics of the finishedsand core. Generally, sand core mixtures consist, by weight, ofapproximately 2.0% to 3% water, 0.75 to 1.2% core oil binder, 0.75% to1.25% cereal binder and the balance substantially all sand. A typicalmixture which can be used comprises 2% by weight of water, 1% by weightof core oil binder, 1% by weight of cereal binder and the balancesubstantially all sand.

After mixing, the sand is compacted, usually by blowing, into thedesired form in a suitable mold or core box. The core thus formed isthen removed from'the core box and baked or cured at an elevatedtemperature for approximately one to three and one-half hours. Any finswhich have been formed on the surface of the core are removed after thecuring operation. In accordance with this invention a low pressure sandblast is directed onto the fin of the cured core, preferably atsubstantially right angles to the fin. It is preferred to direct thesand blast generally parallel to the adjacent surface of the sand coreand at substantially right angles to the major surfaces of the fin beingremoved. By such action the sand blasting particles directly impinge ononly the principal ex posed surface of the fin, thereby reducing thepossibility of deleterious effects on the core surface itself. The sandblast is under an air pressure which is high enough to remove the fin,yet sufficiently low that abrasion of useful core surfaces isnegligible.

The pressure to be employed in removing fins from sand cores primarilydepends upon the hardness of the core surfaces which in turn dependsupon the composition of the sand mixture. For example, sand cores havinga relatively high proportion of binder and core oil will produce a sandcore having a surface which is comparatively hard. A low proportion ofthese constituents in the sand mixture will produce a sand core having asurface which is relatively soft.

Referring more particularly to the drawings, Figure 1 schematicallyshows an apparatus which can be used to practice this invention. Sand ina storage hopper or magazine lit is conveyed to a standard sand blastingnozzlelzby a connecting conduit 14 which communicates with a port in alower portion 16 of the hopper. Conventional sand blast nozzles areinternally constructed to function as a jet pump. Compressed air,introduced into the nozzle by the attached hose 18, produces a partialvacuum in the nozzle which is used to draw the sand from the storagecabinet into the compressed air stream 20. The amount of sand beingdrawn to the nozzle can be varied by adjusting a slip collar 22 aroundthe sand delivery conduit. The collar 22 covers an aperture (not shown)in the conduit 14 and can be adjusted to expose part orall of theaperture. Adjustment of the collar 22 affects the amount of air enteringthe sand delivery conduit and correspondingly affects the amount of sanddrawn from the storage hopper It A cured sand core 24 is positioned on asuitable supporting rack 26 in a sand collection cabinet 27 in such amanner that the sand blast 21) is substantially at right angles to thefin 28 which is to be removed. The lower wall 30 of the sand collectioncabinet 27 slopes downwardly toward its center to a sand collectionaperture (not shown). A suction line 32 conveys the sand from acollecting device 34 in the aperture to the storage hopper 16. A jetpump 36 is attached to the line 32 to provide the required partialvacuum conditions to draw the used sand up the return line forrecycling.

The impingement of a sand blast 26 on a fin 28 of a sand core 24 isshown in Figure 2. In most instances, superior results are obtained ifthe sand blast 20 is substantially at right angles to a major surface ofthe fin 28 and generally parallel to the adjacent surface of the coreitself. Such action produces a substantially complete removal of thetin, such as shown in Figure 3.

The limiting ranges of the air pressure employed for the sand blast arecritical and the specific preferred air pressure is dependent upon thehardness of the core surface, the thickness of the fin, etc. Usually,the highest air pressure which can be used is dependent upon thehardness of the core and can readily be identified by a pitting of thecore surface. In most instances the definning can be accomplishedsatisfactorily with an air pressure of two to six pounds per square inchwhen using silica sand. A sand blast under an air pressure of fourpounds per square inch is generally preferredfor definning most sandcores.

This method of definning sand cores can readily be adapted to acontinuous and automatic operation, such as required for modern highproduction of materials. The sand core can be placed on a moving.conveyor and passed through a sand blast apparatus similar to that shownin the drawings. The sand core is automatically definned as it iscarried continuously through the sand blast region. Although in manyapplications a single sand blasting nozzle can be used to remove thefins from a core, in some instances it is more advantageous to employ aplurality of sand blasting nozzles. A plurality of sand blasting nozzlescan be strategically located in a sand blast cabinet so that each iseifectively directed to defin a particular part of the core as it passesthrough the sand blast region.

This method is further applicable to definning sand cores other thanthose made in the conventional manner hereinbefore described and, forexample, may be used to defin some shell mold sand cores. A shell coreis a relatively thin-walled hollow structure made from a mixture whichconsists essentially of sand and a thermosetting resin binder. Themolding material generally used is a dry mixture comprising a majorproportion of silica sand and a minor proportion (1% to by weight) ofthe thermosetting binder. Phenol formaldehyde and melamine formaldehyderesins are typical examples of the type of thermosetting resin binderused. The sand employed is preferably free of metal oxides, claymoisture and organic matter.

A shell molded sand-resin core can be produced by a method such asdisclosed'in United States Patent No. 2,688,780 in the name of Arthur I.Anderson. This patent teaches a method of making sand-resin cores whichinvolves allowing the dry mixture of sand and resin powder to come intocontact with the surface of a hot metal core box for a short period oftime. A layer of the mixture adheres to the heated metal surface due toa plasticizing of the resin which entraps the sand with which it isintimately mixed. The resin is then hardened or thermoset to stabilizethe mixture to accurately reproduce core box details.

The sand-resin mixture is blown into the heated core,

box under an air pressure of approximately 40 to 50 pounds per squareinch where it adheres to the heated walls of the core box. The blowingis continued until a core wall of sutficient thickness is formed. A moldtemperature range of approximately 250 F. to 450 F. is generallysuitable although, in some instances, temperatures up to approximately800 F. can be employed. In most instances, a temperature ofapproximately 350 F. appears to be satisfactory.

The blowing time may vary considerably, of course, but blowing times ofa few seconds to about fifteen seconds have been satisfactorilyemployed. The actual blowing time which is to be employed frequentlydepends upon the desired wall thickness; hence, longer blowing times maybe necessary to form cores having exceptionally thick walls.

Following the blowing operation a short time interval may be allowed forthe thermosetting resin binder to set or plasticize in the core box, aperiod of time ranging from a few seconds to approximately one minutebeing appropriate for various applications. A build-up time in the orderof about ten seconds is usually sufiicient to form core walls ofsatisfactory thickness, and oftentimes the setting of the resin willtake place to a sufiicient extent during the short blowing period thatan additional setting time is unnecessary. The core is then cured whilestill in the mold at a temperature between approximately 550 F. andapproximately 1300" F. A satisfactory baking or curing of the core cangenerally be effected at a temperature of approximately 650 F. After thecore has been cured in the mold, it is stripped therefrom, thuscompleting the operating cycle.

Aswith conventional cores, shell cores are generally made in amulti-piece core box, and hence fins are also frequently found on thesurfaces of shell cores. These fins can sometimes be removed byemploying a relatively low pressure sand blast directed at substantiallyright angles to the surface of the fin. As hereinbefore mentioned,various factors will determine the optimum air pressure which can beemployed in the sand blast. However, for most shell mold sand-resincores, an air pressure of approximately two to six pounds per squareinch has provided satisfactory results. In general shell mold sand coresare efiectively definned by a sand blast under an air pressure ofapproximately four pounds per square inch.

In most applications of this'invention a conventional sand blast nozzle,such as those known in the art, can be employed. Typically, aconventional sand blast nozzle having an outlet orifice of inch indiameter is particularly suitable.

It-is understood that although this invention has been described inconnection with certain specific examples thereof, no limitation isintended thereby except as defined in the appended claims.

We claim:

1. A method of removing a fin projecting from a sand core whichcomprises directing a sand blast under an air pressure of about twopounds per square inch to about sixpounds per square inch substantiallyperpendicularly against a major surface of a fin projecting from a curedsand core and generally parallel to the surface of said core from whichsaid fin projects.

2. A method for the continuous and automatic removal of fins projectingfrom a foundry sand core which comprises placing a cured sand core on aconveyor and moving. said sand core through a plurality of sand blastswhich are under an air pressure of about two pounds per square inch toabout six pounds per square inch wherein each of said sand blasts isdirected to impinge substantially perpendicularly against a majorsurface of a fin and generally parallel to the surface of said core fromwhich said fin projects. 7

3. A method of making a dry sand core which comprises the steps ofcompacting a mixture of sand, water,

core oil binder and cereal binder in a suitable core box to form a core,removing said core from said core box, baking said core at an elevatedtemperature, and thereafter directing a sand blast under an air pressureof about two pounds per square inch to six pounds per square inchsubstantially perpendicularly against a major surface of a fiinprojecting from said sand core and generally parallel to the surface ofsaid core from which said fin projects to thereby remove said fin fromsaid core.

4. A method of making a foundry core which comprises the steps ofcoating 21 hot metal pattern with a mixture of sand and thermosettingresin, allowing said mixture to remain in contact with said hot metalpattern for a sutficient time to plasticize the resin and accuratelyreproduce pattern details on the sand core, heating said core at anelevated temperature which is suflicient to convert said resin to athermoset condition, removing said sand core from said heated pattern,and thereafter directing a sand blast under an air pressure of about two6 v, pounds per square inch to six pounds per square inch substantiallyperpendicularly against a major surface of a fin projecting from saidsand core and generally parallel to the surface of said core from whichsaid fin projects to thereby remove said fin from said core.

References Cited in the file of this patent UNITED STATES PATENTS554,473 Beeg Feb. 11, 1896 999,485 Carolin Aug. 1, 1911 1,503,586Hileman' Aug. 6, 1924 2,448,316 Lesavoy Aug. 31, 1948 2,483,956 WorkmanOct. 4, 1949 2,507,390 Wallace May 9, 1950 2,618,109 Miller Nov. 18,1952 2,688,780 Anderson Sept. 14, 1954 FOREIGN PATENTS 935,149 GermanyDec. 29, 1955

